2018gaokao

3b1b.py

from manimlib.once_useful_constructs.region import Region
# PMobject 有 filter_out 方法，Circle 没有
class SquareToCircle(Scene):
    def construct(self):
        circle = Circle()
        a = ORIGIN
        pointB = Dot(point=np.array([-0.5042, 0.8636, 0]))

        centerB = np.array([-0.7521, 0.4318,0])
        semi_circleA = Arc(angle=np.pi, radius=1)
        semi_circleB = Arc(angle = np.pi, radius = 0.4979,
                           arc_center=centerB)
        semi_circleC = Arc(angle = np.pi, radius = 0.86722,
                          arc_center=np.array([0.2479, 0.4318,0]), start_angle=(-29.8622) * np.pi / 180 )


        circleB = Circle(radius = 0.4979,
                         arc_center=centerB)

        # half a circle
        interior = Region(lambda x, y : (x**2 + y**2 < 1) & (x > 0))

        pic = VGroup(semi_circleA, semi_circleB, semi_circleC, pointB)
        square = Square()
        square.flip(RIGHT)
        square.rotate(-3 * TAU / 8)
        circle.set_fill(PINK, opacity=0.5)

        # self.play(FadeIn( semi_circleA), run_time=2)
        # self.play(FadeIn(pic.scale(3)), run_time=2)

        self.play(FadeIn(interior), run_time=2)
        # self.play(Rotating(circle.scale(3)), run_time=2)